1. Field of the Invention
The present invention relates to an automatic packaging method and, more particularly, to improvement in or relating to a method by which articles to be packed and being conveyed, e.g. such as by flights of conveying means, are successively put into a tubular bag of a film of synthetic resin or a suitable plastic material.
2. Description of the Prior Art
One typical packaging machine which is widely employed for automatic packaging of articles is a horizontal pillow type machine as shown in FIG. 1. This type automatic packaging machine comprises a conveying unit 3 equipped with flights 2 for conveying articles 1 to be packaged at predetermined intervals, an end sealer 4 disposed downstream of the conveying unit 3, and a film supply reel 6 having wound thereon a band-shaped film 5, e.g. such as of synthetic resin or a suitable plastic material. A plurality of film guide rollers 8 are disposed between the film supply reel 6 and the conveying unit 3, and a bag-making device 9 is disposed at a position adjacent the downstream end of the conveying unit 3. The film 5 wound on the supply reel 6 is drawn out therefrom and guided by the guide rollers 8 to the bag-making device 9, wherein it is formed into a continuous tube 10. The conveyer unit 3 includes an endless chain 11 to which the flights 2 are attached for movement therewith. Each article 1 is placed on the endless chain 11 with its rear end being in contact with the flight 2, so that the article 1 is forwarded from the left-hand side to the right-hand side in FIG. 1 as the endless chain 11 moves. At the downstream end of the conveying unit 3 the article 1 is received into the bag-making device 9 and is introduced into the film tube 10. Thereafter, the article 1 is carried by the film tube 10 to the end sealer 4 which is adapted to cut and seal the film in the transverse direction at a predetermined pitch, hereinafter referred to as the cut-pitch.
The traveling or running speed of the conveying unit 3 should be coordinated with the traveling or running speed of the end sealer 4 so that the latter may cut and seal the film at points between the adjacent articles 1. Usually, the pitch of the flights 2 is selected to be sufficiently large in order to permit articles of various sizes to be carried thereby, and therefore it is larger than the cut-pitch unless the article is of maximum size. Consequently, in the conventional machine the running speed of the conveying unit 3 is set higher than the traveling speed of the film tube 10 to make it possible to supply the articles 1 into the film tube 10 at a time interval during which the film travels a distance equal to the cut-pitch.
Such a higher speed of the conveying unit 3, however, causes the article 1 to be thrust into the film tube 10. Therefore, if the articles 1 are of a material having a small coefficient of friction, they tend to advance slidingly relative to the film tube 10 due to the force of inertia, thereby resulting in the articles 1 being placed at positions different from the intended positions between the adjacent cut points. On the contrary, if the articles 1 are of a material having a large coefficient of friction, they will not smoothly move into the film tube 10 and will tend to be jammed at the inlet of the device 9. Furthermore, in the case where the articles 1 are larger in height than the flights 2 and are liable to lose their shape, such as stacked ham slices, since only the upper portions thereof will rub against the film tube 10, the articles 1 will readily get out of shape when put into the film tube 10. These problems become more and more serious with an increase in the running speed of the machine for increasing the efficiency of a packaging operation.
It is therefore an object of the present invention to provide an automatic packaging method which is free from the above-mentioned defects of the prior art and which permits optimum automatic packaging for articles of various sizes.